The present invention relates to network protection architectures in general, and ring interworking architectures in particular.
ITU-T Recommendation G.842 (April 1997) entitled xe2x80x9cInterworking of SDH Network Protection Architecturesxe2x80x9d (hereinafter referred to as xe2x80x9cG.842xe2x80x9d and whose contents are incorporated by reference) discusses dual ring network protection architectures including inter alia a form of dual node interconnection termed ring interworking. One implementation of ring interworking is the so-called SubNetwork Connection Protection (SNCP) ring interworking architecture which is characterized by its top ring and its bottom ring being mirror images of one another.
Generally speaking, the term ring interworking refers to a dual ring network topology which includes top and bottom rings each having an I/O node with a transmit tributary and a receive tributary, two west working channels between the I/O node and an west interconnection node from the perspective of the top ring, and two east protection channels between the I/O node and an east interconnection node from the perspective of the top ring. The terms xe2x80x9cworking channelxe2x80x9d and xe2x80x9cprotection channelxe2x80x9d are purely descriptive to distinguish between two identical channels except that a ring""s working channel is typically its default active channel in terms of signal flow therealong. Only one of a ring""s working and protection channels may be active in terms of end-to-end signal flow therealong at any one time, if at all.
The opposite west interconnection nodes of the top and bottom rings define a west interconnection interface and, similarly, the opposite east interconnection nodes of the top and bottom rings define an east interconnection interface. Each interconnection interface has a pair of lines bridging across the rings, one of which is employed as a so-called top down receive line from the transmit tributary of the top ring""s I/O node to the receive tributary of the bottom ring""s I/O node via either a top down west working channel or a bottom up east protection channel. Conversely, the other line is employed as a so-called bottom up transmit line from the transmit tributary of the bottom ring""s I/O node to the receive tributary of the top ring""s I/O node via either a bottom up west working channel or a bottom up east working channel.
It is a commonly purported that ring interworking and, in particular, a G.842 compliant SNCP ring interworking architecture provides top down fiber optic network survivability as long as one of the top ring""s top down working or protection channels, one of the bottom ring""s top down working or protection channels, and one of the east or west interconnection interfaces"" receive lines remain intact. However, topological analysis of a G.842 compliant SNCP ring interworking architecture reveals that the east and west interconnection interfaces"" receive lines are each connectable to the receive tributary at the bottom ring""s I/O node from their respective sides only from the perspective of the top ring, namely, the west interconnection interface""s receive line is only connectable to the bottom ring""s I/O node from the west and conversely the east interconnection interface""s receive line is only connectable to the bottom ring""s I/O node from the east. Due to this, a G.842 compliant SNCP ring interworking architecture cannot provide top down fiber optic integrity in the case of a double fiber optic failure involving the west interconnection interface""s receive line and the bottom ring""s east protection channel nor the east interconnection interface""s receive line and the bottom ring""s west working channel.
The above analysis equally applies to bottom up fiber optic network survivability by virtue of the symmetrical nature of a G.842 compliant SNCP ring interworking architecture.
There is a need to provide a network protection architecture with fiber optic network survivability capabilities above and beyond those of a G.842 compliant SNCP ring interworking architecture.
In accordance with the present invention, there is provided a network protection architecture comprising:
(a) a top ring with an I/O Node A having a transmit tributary TTA and a receive tributary RTA, a top down west working channel WCAB, a bottom up west working channel WCBA, a top down east protection channel PCAC, a bottom up east protection channel PCCA, and two double switch interconnection nodes B and C;
(b) a bottom ring with an I/O Node Z having a transmit tributary TTZ and a receive tributary RTZ, a top down west working channel WCDZ, a bottom up west working channel WCZD, a top down east protection channel PCEZ, a bottom up east protection channel PCZE, and two double switch interconnection nodes D and E;
(c) said interconnection nodes B and D having a receive line RLBD and a transmit line TLDB bridging thereacross;
(d) said interconnection nodes C and E having a receive line RLCE and a transmit line TLEC bridging thereacross;
(e) said interconnection node B having switches S1 and S5, said switch S1 switching said receive line RLBD between said working channel WCAB between and said protection channel PCAC, and said switch S5 switching said working channel WCBA between said transmit line TLDB and said transmit line TLEC;
(f) said interconnection node C having switches S2 and S6, said switch S2 switching said receive line RLCE between said working channel WCAB and said protection channel PCAC, and said switch S6 switching said protection channel PCCA between said transmit line TLDB and said transmit line TLEC;
(g) said interconnection node D having switches S3 and S7, said switch S3 switching said transmit line TLDB between said working channel WCZD and said protection channel PCZE, and said switch S7 switching said working channel WCDZ between said receive line RLBD and said receive line RLCE; and
(h) said interconnection node E having switches S4 and S8, said switch S4 switching said transmit line TLEC between said working channel WCZD and said protection channel PCZE, and said switch S8 switching said protection channel PCEZ, between said receive line RLBD and said receive line RLCE.
The network protection architecture of the present invention is based on the realization that a G.842 compliant SNCP ring interworking architecture with additional limited switching capability can provide full top down and bottom up fiber optic network survivability in the face of all fiber optic failures except truly catastrophic failures.